ΠΜΣ με ειδίκευση στην Εφαρμοσμένη Περιβαλλοντική Γεωλογία
Library of the School of Science

2012-12-14

2012

Τζίφας Ιωάννης

Αθαν. Γκοντελίτσας Επίκ. Καθηγητής ΕΚΠΑ (Επιβλέπων), Ανδ. Μαγκανάς Καθηγητής ΕΚΠΑ, Μαρ. Βλάχου-Τσιπούρα Επίκ. Καθηγήτρια ΕΚΠΑ

Ορυκτοχημεία ακτινίδων σε ιζηματογενή πετρώματα της Δ. Ελλάδας

Greek

Mineral-chemistry of actinides in sedimentary rocks of W. Greece

Epirus region (NW Greece) is generally composed of Mesozoic (250-65 million
years old) sedimentary rocks of Ionian zone, derived from the Tethys
paleo-Ocean. The sedimentary rocks are mostly limestones and shales which are
fundamentally poor in U (<0.1, 2.2 and 3.5 ppm) and therefore no elevated
concentrations would be expected in Epirus region. However, it is known
(internal reports from Greek Atomic Energy Commission and IGME) that in some
areas the natural radioactivity is high due to the presence of
phosphate-bearing sedimentary rocks (phosphorites). Phosphorites are marine
sediments containing an average of 120 ppm U, and may significantly contribute
in U geochemical anomalies. Additionally, they are rich in light rare-earth
elements/LREE, but not in Th (6.5 ppm) and other HRRE. Uranium in the ocean
waters (3.2 ppb) follows anoxic pathways and it is mainly removed from the
solution by chemical processes taking place at the interface of organic-rich
sediments. It is therefore correlated to organic carbon whereas the diagenetic
cycle of the element may include reduction of U6+ to U4+ related to sulphate
bio-reduction. Samples from Epirus region concerning laminated phosphatized
limestones (sample: DRYM1), bedded chert-rich limestone (sample: PER1) and
tectonized/re-processed phosphatized limestone (sample: PER2), were scanned in
the field using a portable radiation detector. Bulk geochemical analyses using
ICP-OES/MS showed variable U concentrations with a notable value of 648 ppm in
the case of the dark organic-rich part of the sample PER2. Gamma-ray
measurements using HPGe showed that the above geological materials exhibit high
radioactivity mainly due to the 238U-series. The 238U content was determined by
the counts in the 1001-keV photopeak of the daughter 234mPa (7700 Bq/Kg).
Powder-XRD, SEM-EDS and further chemical analyses indicated abundant apatite
and organic matter, besides calcite, which should be associated to the high U
content. Relatively high concentrations of Cd, probably related to apatite,
were also revealed. On the other hand, the rock is geochemically depleted in
LILE (e.g. Cs, Rb, K), as well as in As, Sb and Se in contrast to “average
phosphorite”.

Epirus, Phoshosphates, Uranium, Actinides

No

0

Yes

363

237

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https://pergamos.lib.uoa.gr/uoa/dl/object/1319300